The present invention relates to a staging (or data rereading) method and system, and more particularly to a staging method and system capable of shortening a search time when data are read and retrieved or searched from an unrewritable and removal medium such as an optical disk.
As the conventional staging method is known a reading method disclosed in No. JP-A-57-13546. According to this method in which data are read from a sequential file having keyed records, the reading of blocks is carried out by recording the positions of the first and last records in each block and referring to the position information. Namely, node numbers (i.e., key information of records) of the first block to the last block are first written in a staging designation range setting device. Thereafter, all the records 1 to n are read so that the position information is written in a record position register while the reading of the first block is performed. Since the position numbers of the first and last records in each block are thus written in the record position register, the reading of the second block and the subsequent blocks is made referring to those position numbers. In this method, the number of times of reading equal to the total number of records plus the number of records in the second and subsequent blocks is required.
In the above-mentioned conventional method, only the reading from a medium such as a magnetic tape or magnetic disk to which the writing has been made, is taken into consideration. No consideration is taken to a removal and unrewritable medium such as an optical disk. For such a medium, therefore, in the case where the medium subjected to any alteration or modification such as addition, updating and/or deletion by another device is again processed, it is necessary to read over the entire file again from the beginning to the end.
In an electronic file device using an optical disk, alteration such as addition, updating and/or deletion is effected by additionally or annotatively recording alteration information on a blank region of the optical disk.
In the electronic file device, when a plurality of optical disks are searched at once, titles on the optical disks, for example, names added to picture images are preliminarily staged on a staging file including a non-volatile memory such as a magnetic disk, a desired title is searched from the titles staged on the staging file, and a picture image data corresponding to the searched or located title is read from one of the optical disks. In that case, if any alteration such as addition, updating and/or deletion is to be made, data of both the optical disks and the staging file should be simultaneously altered, thereby preventing any deviation or anti-coincidence of data between the optical disks and the staging file. However, if the optical disk is removed after the staging and the alteration such as addition, updating and/or deletion is made to the optical disk in another electronic file device, the optical disk would have information of the alteration additionally or annotatively recorded thereon. Therefore, a deviation or discrepancy exists between the information on the optical disk and the data in the staging file on which the data were previously staged. Accordingly, staging must be carried out again for searching of picture image data. As a result, a time required for reading of data is remarkably elongated.
Further, in the case where an electronic file (device) is used in common by a plurality of terminals or retrieval devices, the fact that the time necessary for the staging for each terminal is long, obstructs the access from the other terminals, thereby lowering the availability and operation rate of the electronic file (device).